Re: New to forum
Welcome to the forum. We have a DYI (Do it Yourself) section that caters to non kit builders that you might enjoy. There are plenty of engine options available and your concept doesn't sound like anything that hasn't been tried, or done before.
45mph might be a little optimistic but who knows what you might acheive with the right gearing? Show us some photos of your project as it progesses.
Good luck, have fun and ride safe.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"